1. Field of the Invention
The present invention relates to an original scanning apparatus for scanning an original, and particularly, to an apparatus having a reflecting member for reflecting light from an original.
2. Description of the Related Art
A reading optical system in an image reading apparatus functioning as an original scanning apparatus is constituted of a light source, a reflecting mirror, a lens, a reading sensor and the like.
Conventional image reading apparatuses include the following two types. One is an image reading apparatus with an optical system of an integral optical carriage system that has all elements of the optical system in one optical carriage. The other is an image reading apparatus with an optical system of a mirror movement system in which a lens and a reading sensor are fixed to a main body of the image reading apparatus and a first optical carriage having a light source and a mirror and a second optical carriage having a plurality of mirrors move while keeping a fixed optical path length.
In both the image reading apparatuses, in order to cause reflected light from an original to be accurately incident on a reading sensor, positions and angles of a plurality of mirrors for guiding light to the reading sensor need to be set in a carriage with extremely high accuracy.
In general, a mirror is a plate-like reflecting member and supported on supporting means by three-point support and this supporting means is fixed to a carriage.
In addition, a carriage of an optical system is generally formed of a resin material because it has advantages in terms of molding characteristics, costs, weight and the like.
Incidentally, the carriage has a light source and a heat source such as an inverter for driving the light source. Thus, when reading of images is continued for a long time, temperature of the carriage rises to cause deformation of resin.
Then, when the resin material is deformed by expansion or the like due to thermal deformation, supporting portions of reflecting mirrors move and deform, whereby positions and angles of the mirrors change to cause such a problem in that reflected light from the mirrors is not incident on a reading sensor accurately.
In particular, in an image reading apparatus according to an image flow reading system which is provided with an automatic feeding mechanism of an original and reads an image by moving an original in a state in which an optical system is fixed, since the optical system is continuously in a reading state while a plurality of originals set in the automatic feeding mechanism are read, deterioration of reading accuracy due to the rise of temperature is a critical problem.